package com.tonytaotao.algorithm;

import java.util.Arrays;

public class KMP {

    public static void main(String[] args) {
        String str1 = "BBC ABCDAB ABCDABCDABDE";
        String str2 = "ABCDABD";

        int[] next = kmpNext(str2);
        System.out.println(Arrays.toString(next));

        System.out.println(kmpSearch(str1, str2, next));

    }

    /**
     *
     * @param str1 源字符串
     * @param str2  子串
     * @param next 子串对应的 部分匹配表
     * @return
     */
    public static int kmpSearch(String str1, String str2, int[] next) {
        for (int i = 0, j = 0; i<str1.length();i++) {

            while (j > 0 && str1.charAt(i) != str2.charAt(j)) {
                j = next[j-1];
            }

            if (str1.charAt(i) == str2.charAt(j)) {
                j++;
            }

            if (j == str2.length()) {
                return i - j + 1;
            }
        }

        return -1;
    }

    public static int[] kmpNext(String dest) {
        // 创建一个next数组保存部分匹配值
        int[] next = new int[dest.length()];
        next[0] = 0; // 如果字符串是长度为1，部分匹配值为0

        for (int i = 1, j = 0; i < dest.length(); i++) {

            while (j > 0 && dest.charAt(i) != dest.charAt(j)) {
                j = next[j-1];
            }

            if (dest.charAt(i) == dest.charAt(j)) {
                j++;
            }
            next[i] = j;
        }

        return next;
    }

}
